Stretch forming machine



July 10, 1956 B. F. RAYNES 2,753,915

STRETCH FORMING MACHINE Filed Feb. 9. 1953 2 Sheets-Sheet 1 y 0, 1956 B. F. RAYNES 2,753,915

STRETCH FORMING MACHINE Filed Feb. 1953 2 Sheets-Sheet 2 INVENTOR.

United States Patent STRETCH FORMING MACHINE Burt F. Raynes, Chula Vista, Caliil, assignor to Rohr Aircraft Corporation, Chula- Vista, Calif., a corporation of California Application February 9, 1953, Serial No. 335,933

2 Claims. (Cl. 153-48) This invention relates to a machine for stretch forming metal to a desired shape by stretching the metal over a curved die.

Machines for stretching large sheets to a desired shape must necessarily apply large forces and are consequently massive and expensive to construct. It is therefore desirable that such machines be adapted for universal use for the making of parts of various shapes and sizes. It is accordingly an object of this invention to provide a forming machine capable of stretching metal sheet to a wide variety of shapes and sizes. This is preferably done by providing members capable of being mounted in a known type of metal press and effecting the metal forming when the press is operated.

In the stretching operation, jaw holders that have jaws which gripthe edges of the metal sheet are used, and when used with dies of different widths, it is necessary that the jaw holders be located at different distances from the front-to-rear horizontal center line of the press. It is accordingly another object of the invention. to provide adjustable means whereby the jaw holders may be set to accommodate dies of different widths and lengths and wherein. the jaw holders may be set along the curved contents of any die whose width is different at diflerent points along its length.

When used with a die of curved contour, the jaws when in gripping position do not. lie in a common plane and it is accordingly another object of the invention to provide for the pivotal mounting of the jaw holders for universal movement in any direction. This type of pivotal mounting permits the jaw holders to accommodate themselves to the direction of the pull in the metal as the stretching proceeds.

A still further object isto provide a convenient control means arranged to operate all the jaws which grip one edge of the sheet simultaneously.

Other objects will become apparent as-the description of the machine proceeds. For a better understanding of the invention, reference is made to the accompanying drawing inwhich:

Figure l is a perspective view of a stretch forming machine embodying the'invention;

Figures 2 and 3- are front views of the machine showing a workpiece in diiferent stages of the forming operation,

Figure 4 is a cross sectional view through a workpiece holder and a portionof its support and,

Figure 5 is a sectional view through line 5-5 of Figure 4 showing the lower portion of the workpiece holder.

The invention is illustrated in connection with a known type of press for forming a thin metal sheet as, for example, of aluminum alloy over a convex male die 11 which is supported on a die plate 12 mounted at the top of several supporting columns 13 which are in turn supported on stationary bolster plate 21. When forming skin members for airplanes the die 11 is often made with a re inforcing metal framework 14 covered by a mass of hardened plaster 15 or other plastic material which has been molded to the exact desired contour while in a plastic 'ice condition. and then permitted to set hard. In a thermosetting plastic is used, the die is heated at a suitable temperature to set it. In any case, the upper convex surface 16 of the die is hard and has the shape to which the finished sheet 10 is to be conformed. The die 11 illustrated is substantially wider' at the near than at its far end and the clamp holders 17 which stretch the sheet are arranged at the commencement of the forming operation outwardly from the die, as shown in Figure 2. The clamp holders are supported on a pair of similar supporting. beams 1819, each of which is attachedto and supportedfor vertical movement on a set of pressure pins 20 slidable through a stationary bolster plate 21. Plate 21 is supported on the bed or base 22 of the press which is hollow and contains hydraulic or pneumatic cylinders (not shown) within which the lower ends of pins 20 extend. and are slidable, in a known manner. The beams 1819 are connected together by spaced apart connecting beams 18', only one of which is shown in Figures 2 and 3, and are forced down by two or more driving columns 23, the upper ends of which are attached to the actuating ram 24. which is raised and lowered by power driving means (not shown) in a known manner. Ram 24 is lowered on its power stroke at a speed which is suitable for the particular metal. composing workpiece 10.

To provide for the adjustment of. clamp holders 17 toward and away from die 11, the support beams 1819 are provided, as shown, with a set of T-shaped slots 29 in which blocks 30 are sl'idably mounted. (See Figures 4 and 5.) Each block 30- is clamped in proper position by a slide 31 disposed inslot 29 and tapped to receive a pair of bolts 32 which pass through a pair of short bars 3-3 that span the slot 29 and are seated on top of the support beam Each clamp holder 17 is mounted for universal pivotal movement in any direction by means of a. pin 34 having an enlarged foot 35 resting on slide 31, pin. 34 being rotatable. about a vertical axis in block. 30 and the main. body portion 36 of the jaw holder being pivotally connected. to pin 34 by a horizontal connecting pin 37. As shown in Fig. 1, the bottoms of columns are spaced outwardly from clamp holders 17 and blocks 30 to permit adjustment of blocks 30 in slots 29 toward and away from die 11.

Each clamp holder and clamp is preferably of the c011- struction shown and claimed in U. S. Patent to M. B. Laddon et al., No. 2,702,929 issued March 1, 1955 but it will be understood that this invention is not limited to the use of this particular type of clamp. The clamp illustrated is hydraulically operated by means of fluid supplied under pressure through flexible rubber conduits 38, 39 to a point below or above a piston 4t) slidable Within a cylinder 41 bored in body portion 36. Piston 40 actuates a piston rod 42 having an enlarged head 43 seated in correspondingly shaped slots in a pair of clamp jaw holders 44 which are slidable along, a pair of bearing rotors 45 seated for rotation in body 36. Each jaw holder 44 is cut away, as shown, to receive a projecting foot 46 on the lower end of the jaw 47,, a pair of the jaws 47 having parallel faces which grip the opposite faces of sheet 10 at its lower edge.

Each of the support beams 18 and 19 is provided with an attached fluid supply system which supplies fluid such as oil or water, under pressure to operate all the pistons 40. Each system comprises two metal pipes 48, 49 attached to the beam by brackets 50. Each pipe is provided opposite each clamp holder 17 with a screw threaded outlet 5l'52, the outlets 51 being connected to the ends of flexible tubes 39 and outlets 52 connected to tubes 38 (only two of the tubes being shown). The ends of pipes 48, 49 are connected by rubber tubes 53, 54 to the outlets 55, 56 of a two-way valve (not shown) contained in a casing 57, secured to the end of the support 3 beam, the valve being operated by a control handle 58. Fluid under high pressure is supplied to casings 57 by a flexible conduit (not shown). The far ends of pipes 48- 49 are closed by caps (not shown).

To use the press, die 11 is secured in position on plate 12 and the several blocks 30 moved along the slots 29 to bring the clamp holders 17 into the position shown in Figure 2 where each holder is spaced outwardly of the die. Bolts 32 are then tightened to lock blocks 30 in position. The sheet is then placed over the die and its opposite edges inserted between the several jaws 47. Valve handles 58 are then turned to supply fluid under pressure to pipe 49 and via conduits 38 to all cylinders 41, thereby causing all the pistons 40 to rise and cause clamp jaws 47 to firmly grip sheet 10. The first stage of the forming is then effected by causing ram 24 to descend thereby depressing beams 18-19 and all clamp holders 17 by an amount sufficient to stretch sheet 10 somewhat beyond its yield point and cause the sheet to conform in shape to the upper portion of the die. As the stretching proceeds, each clamp holder 17 is free to move pivotally in any plane required by the tension in that region of sheet 10 as determined by the contour of the die, pivot pin 34 permitting holder 17 to rotate about a vertical axis and pivot pin 37 permitting the holder to rotate about a horizontal axis. Ram 24 is then raised to relieve the tension on the sheet, the edges of the sheet removed from jaws 47, bolts 32 are loosened and blocks 30 slid inwardly along slots 29 to bring clamp holders 17 into positions on beams 18-49 as shown in Figures 1 and 3. The edges of sheet 10 are now inserted in jaws 47, the jaws operated to again grip the sheet and the bolts 32 again tightened. The forming is then completed by causing ram 24 to descend and cause clamp holders 17 to lower into their final positions shown in Figures 1 and 3. This again stretches sheet 10 beyond its yield point and gives it its final set when it has the desired shape of die 11. Ram 24 is then raised permitting pressure pins 20 to lift beams 18-19 and clamp holders 17 thereby lifting sheet 10 slightly above the die. The operator then adjusts handles 58 to admit fluid under pressure to pipe 48 and conduits 39, thereby causing all the pistons 40 to descend and release all the jaws 47 from the finished sheet, which may now be removed from the machine. While the machine is especially adapted to the forming of sheets of aluminum alloys having a thickness of onequarter inch or less, it will be understood that its use is 'not so restricted but that it may be used to form sheets of greater thickness and also sheets composed of other metals or materials capable of being stretched to a desired shape.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment of the invention is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Having thus described my invention, what I claim as new and useful and desire to secure by Letters Patent is:

1. A machine for stretching a metal sheet extending over a stationary convex die comprising, in combination: two spaced apart horizontal supporting plates extending under the die and beyond the sides thereof; a plurality of cylinders carried by each plate; adjustable means whereby the distance between each cylinder and the die may be adjusted; pistons disposed in said cylinders, each of said cylinders having a first inlet disposed above its piston and a second inlet disposed below its piston; two gripping jaws connected to each piston and constructed to engage the edge of the sheet in response to upward movement of the piston and to disengage the sheet in response to downward movement of the piston; two long rigid pipes carried by each supporting plate; flexible conduits connecting one of said pipes to the first inlet of the cylinders on the plate; flexible conduits connecting the other of said pipes to the second inlet of the cylinders on the plate; controllable valve means arranged in one position thereof to supply pressure fluid to two of said pipes to simultaneously raise all said pistons and in a second position thereof to supply pressure fluid to the other two pipes to simultaneously lower all said pistons; a vertically movable ram disposed above said support plates; and a plurality of spaced apart columns depending from said ram and constructed to simultaneously depress said plates and stretch the sheet against the die.

2. A machine for stretching a metal sheet extending over a long convex stationary die into conformity with the die comprising, in combination: a movable support under the die and having a length greater than the length of the die and a width substantially greater than the width of the die, the upper portion of said support being provided with a plurality of inverted T shaped slots termimating in the upper face thereof, said slots extending transversely to the die for a substantial distance out beyond the sides of the die; a block slidable in each slot and having a vertical opening therein; vertical pins having lower portions engaging the marginal walls of said vertical openings for rotation about vertical axes, each block and pin having interlocking portions constructed to prevent upward movement of the pin in its block; jaw holders having openings in the upper ends thereof; horizontal pivot pins passing through the upper ends of said pins and the lower ends of said jaw holders for supporting said jaw holders on the upper ends of said pins for pivotal movement about the horizontal axes of said pivot pins; anchoring means engaging said blocks for anchoring said blocks at positions in said grooves outwardly beyond the sides of the die, said anchoring means being constructed to permit, free rotation of said vertical pins about their axes; pairs of jaws carried by said jaw holders and disposed within said openings at the upper end thereof, said jaws gripping the opposite edges of the sheet; a plurality of spaced apart actuating members engaging said movable support at spaced apart points outwardly of the jaw holders along opposite edges of the sheet; and a vertically movable ram arranged to simultaneously depress said actuating members and jaws a distance sulficient to stretch the sheet against the convex face of the die.

References Cited in the file of this patent UNITED STATES PATENTS 1,164,698 Artz Dec. 21, 1915 1,622,590 Jolstad Mar, 29, 1927 2,084,456 Rode June 22, 1937 2,269,549 Oeckl Jan. 13, 1942 2,279,964 Berliner Apr. 14, 1942 2,346,213 Flowers Apr. 11, 1944 2,428,890 Peterson Oct. 14, 1947 2,437,092 Greene Mar. 2, 1948 2,442,268 Fields May 25, 1948 2,609,860 Kindelberger Sept. 9, 1952 2,702,929 Ladden Mar. 1, 1955 

